Bi-axial stretching machine



1967 O.G. LEWIS ETAL 3,305,889

BI AXIAL STRETCHING MACHINE Filed May 5, 1965 3 Sheets-Sheet 1 INVENTORSOLIVER G. LEWIS HERBERT H. VICKERS HOWARD NORTH ATTORNEY 1967 o. G.LEVT/IS ETAL 3,

BI AXIAL STRETCHING MACHINE Filed May 5, 1965 v 3 Sheets-Sheet 2INVENTORS OLIVER G. LEWIS HERBERT H. VICKERS BY HOWARD C. NORTH QM/FMATTORNEY Feb. 28, 1967 o. G. LEWIS ETAL 3,305,889

I BI-AXIAL STRETCHING MACH INE Filed May 5, 1965 3 Sheets-Sheet 5 1 F|G4FIG. 5

DIRECTION 0F CLAMP 5 TRAVEL INVENTORS OLIVER e. LEWIS 6 HERBERTH.V|CKERS BY HOWARD c. NORTH ATTORNEY United States Patent 3,305,889BI-AXIAL STRETCHING MACHINE Oliver G. Lewis, Westfield, Herbert H.Vickers, Union,

and Howard C. North, Westfield, N.J., assignors to Esso Research andEngineering Company, a corporation of Delaware Filed May 3, 1965, Ser.No. 452,568 10 Claims. (Cl. 181) This invention relates to bi-axialweb-stretching machines in general and in particular to improved meansfor gripping the longitudinal edges of the web as it passes through thestretching zone of the machine.

In machines of this type, as for example, a machine as described in US.Letters Patent No. 3,150,433 issued September 29, 1964 over whichapplicants invention is an improvement, a plurality of individual webclamping means engage the longitudinal edges of the web as the web isfed into the stretching zone. Each of the individual clamping means isfed along diverging guide means to impart a transverse stretch to theweb while it is being pulled longitudinally by the forward motionimparted to the clamping means. At the same time, the longitudinalspacing between adjacent clamping means as they enter the divergentstretching zone is increased so that a longitudinal stretching of theweb will occur at the same time and along with the transverse stretchingperiod. The changing path of travel of the web gripping clamps from anoriginal path parallel to the longitudinal axis of the web whenengagement occurs, into the divergent path in the stretching zone, incombination with the increased spacing between adjacent clamps as theclamps progress through the stretching zone imparts a changing set ofstress conditions to the web in the clamped area. In machines of thetype described in the aforementioned patent, unduly large stressconcentrations are experienced in the web adjacent to clamps to such -adegree that failure and breakage of the web in the clamp area isfrequently experienced. Even in the instances where failure does notoccur with clamps not incorporating applicants invention the inabilityof these prior art clamps to adjust and equalize the stressconcentrations along the edge of the web contributed to non-uniformstretching parameters upon the web during its passage through thestretching zone.

' In accordance with the present invention, the improved clampsdescribed herein are provided with a pivot to allow them to be in effectself-aligning in the direction of the composite forces acting upon theedge of the web. In this way, even though when they initially engage theedge of the web they are aligned parallel to the lengthwise axis of theweb they are able to continue to be oriented in a similar relationshipeven after they have assumed their divergent path of travel in thestretching zone. Furthermore, this ability to pivot about a verticalaxis permits the clamp to assume an orientation imparting the leastamount of stress concentration to the web edge. Each clamps ability topivot also revents binding of the clamp in the guideways thereby greatlyreducing the friction between these elements. Another feature ofapplicants improved clamp is the provision of novel curved serrations onthe gripping jaw. The serrations formed in the jaw face are oriented sothat their curvature conforms substantially to the direction of stressalong the edge of the web and thereby permits the equalization of stressin the web edge between adjacent clamps as the distance between adjacentclamps varies as they progress through the stretching zone. A furthernovel feature of the invention is the provision of improved mountingmeans for the body portion of the clamp relative to the divergent guidemeans so that the body portion of the clamp does not rotate in ahorizontal and/or vertical plane relative to the guide means therebyreducing 3,305,889 Patented Feb; 28, 1967 the overall wear of the clampmeans and reducing their tendency to bind.

Accordingly, it is a principal object of this invention to provide animproved clamp means which reduces the stress concentrations along theedge of the web as it traverses through a stretching zone.

Another object of the invention is to provide an improved clamp meansfor use in apparatus of the type described wherein the clamping means iscapable of pivotable movement relative to its path of travel to permitit to be self-aligning with the stress vectors in the web edge.

Another object of the invention is to provide a novel clamp mechanismfor use in a machine of the type described wherein a plurality of curvedserrations are provided on the clamp jaw for engaging the web whichserrations run generally tangent to the edge of the web between adjacentclamps and permit the stretch being imparted to the web to continueunder the face of the clamp allowing for more even stretch throughoutthe machine direction and still not relax the grip in the transversedirection.

Another object of the invention is to provide an improved clamp which isreliable in operation, easy to service, and low in wear.

These and other objects and advantages of the invention will becomeapparent and the invention will be fully understood from the followingdescription and drawings in which:

FIGURE 1 is a somewhat schematic top-plane view of a bi-axial stretchingmachine with which the invention may be used, certain parts beingomitted for clarity of illustration and other parts being partly brokenaway;

FIGURE 2 is an enlarged fragmentary sectional view taken along lines 2-2of FIGURE 1;

FIGURE 3 is an enlarged fragmentary perspective view showing several ofthe novel clamping means in accordance with the invention as they areadvanced through the stretching zone;

FIGURE 4 is a vertical cross-section of an individual clamping means inaccordance with the invention taken generally along lines 44 of FIGURE3;

FIGURE 5 is a fragmentary sectional view taken substantially along lines55 of FIGURE 4;

FIGURE 6 is a fragmentary plane view of an edge portion of the webshowing the curved stretched portions thereof adjacent each clamp; and

FIGURE 7 is a cross-sectional view taken along line 77 of FIGURE 4.

Referring to the drawings, and in particular to FIG- URE 1, the machinecomprises a main frame structure designated generally at 10. The frame10 supports infeed guide rolls 12 and a discharge conveyor roll system14 for respectively receiving and guiding a web 16 to be stretched intoand from the machine. The frame 10 supports two pair of parallel closedloop guide tracks 18 and 20. Both pairs of tracks are identical exceptthat one is a mirror image of the other, as will be obvious to thoseskilled in the art. The outside track 20 and the inner track 18 areshown in greater detail in FIGURES 2 and 3, which will be referred tohereafter. However, the tracks 18 and 20 are parallel to each other butspaced apart to define a guideway 22 for the web clamping means. (SeeFIGURE 3.) The tracks 18 and 20 are supported on any suitable supportstructure such as for example posts 24 indicated in FIGURE 2. Similarposts not shown are provided for the inner track 18.

The posts 24 which support the track means 18 and 20 are carried bymovable base members not shown which may be laterally adjusted by anyone of three handwheels designated 26, 28 and 30. (See FIGURE 1.) Thosefamiliar in the art, and particularly by reference to the aforementionedpatent, will readily appreciate how adjust- 3 ment of the handwheels 26,28 and 39 affect the lateral spacing of the opposed paths of theirrespectively controlled portions of the tracks 18 and 20. In this way,the amount of lateral stretch imparted to the web 16 may be readilyadjusted.

As shown, the tracks 18 and 20 and the guideway 22 defined therebetweenform a pair of closed loop channels having initial or entrance portions32 substantially straight and parallel to each other, divergent portions34 diverging outwardly from each other in the direction toward thedischarge end of the machine and defining therebetween a stretchingzone, and straight parallel portions 36 defining the discharge ends ofthe guide means. (See FIGURE 1.)

As will be seen most clearly in FIGURE 3 as well as by reference toFIGURE 1, a plurality of clamp assemblies generally designated 38 areadapted to be moved about the, guideways 22 in a circular endless path.Each of the clamping means 38 is advanced through its recirculating pathby the combined action of an endless conveyor 106. a pair of sprocket,wheels at opposite ends of the guide path, as well as by a feed screw 86which advance the individual clamp assemblies 38 in the desired fashionthrough the divergent stretching zone portion of the machine. Referringto FIGURES 3 and 4, each clamp assembly 38 includes a body portion orclamp carrier 40. Each body portion 40 includes a downwardly projectingportion mounting a roller 82 adapted to engage a spiral slot 84 in thefeed screw 86. The feed screw 86 is mounted upon a pivot shaft 88 androtated in conventional fashion to advance each of the individual clampassemblies 38 along the length of the screw. It should be noted that thespiral slot 84 has a varying pitch so that the clamps advanced along thelength thereof gradually become more and more separated to therebyadvance and stretch the film or Web'in the lengthwise direction at thesame time that it is being stretched in the transverse direction. Eachof the clamp carrier portions 40 includes a pair of projecting upper andlower arm or leg portions respectively 42 and 44. t The upper leg 42includes at its outermost ends a pair of guide roller assemblies 46which engage the upper surface of the guide tracks 18 and 20. Similarlythe lower arm or leg portion 44 include like roller assemblies 46 whichengage the lower surface of the guide tracks 18 and 20. A pair ofU-shaped interlocking slipper bearings 48, are disposed about amid-portion of the clamp carrier 40 to provide a longitudinallyelongated wearing surface in the guideway 22. The lengthwise extensionof the slipper bearing surface against the guideway 22 prevents twistingof the clamp canrier 40 and binding therein. Mounted on top of the clampbody portion 48 is a clamp swivel generally designated 50 which ispivotally positioned on the upper stud portion 52. A bushing 54 and abearing washer 56 are provided between the clamp swivel 50 and the pivot52 to reduce friction and to make the swivel rotatable withinpredetermined angular limits relative to the carrier 40. In one form ofthe invention, the desired predetermined angular freedom of the clampswivel 50 relative to the stud portion 52 is selected to be through atotal arc of 45 with freedom forward of the perpendicular to the tracks18 and 20, and 35 rearward of the track perpendicular. Reference shouldbe made to FIGURE 7 in this respect wherein the pivot stud 52 includes aprojecting dove-tail stop lug 68 which engages a similarly shaped butlarger arc recess 70 formed in the swivel 50. As shown, the recess 70extends through an arc of 135 while the stop lug 68 has a 90 segment toproduce the total of 45 angular freedom between these respective pieces.

The upper portion of the pivot 52 includes a slot 58 arranged to receiveone end of a centering torsion spring 64 which is held about the upperend of the pivot by a washer 62 and a C-clip 60. The other end of thetorsion spring 64 extends through a slot 66 formed in the clamp swivel50. In this way the normal position of the clamp assembly under theinfluence of the spring 64 will be in 4 a position perpendicular to thepath of the guide tracks 18 and 20.

Each of the clamp assembly swivels 50 carries a clamp arm 74 pivotallymounted thereto by a pin 72. One end of the clamp arm includes a curvedcamming surface 76 arranged to be mechanically contacted by a camrningplate 77 (see FIGURES 1 and 2) during predetermined portions of theirtravel about the guideways. Each of the clamping arms 74 is normallyheld in a gripping relationship by a pigtail spring means 78 so that thejaw serrations 88 will engage the upper surface of the web 16 at alltimes unless they are otherwise cammed to the open position by the plate77.

Referring to FIGURE 2 the operation and camming of the clamp arms 74 maybe readily understood. In FIG- URE 2, a vertical end shaft 90 will beunderstood to be driven by suitable means not shown. It will be obviousto those skilled in the art how any suitable driving motor may beconnected to the shaft 90 to effect rotation there of while stillpermitting lateral adjustment. Keyed to but slidable on the shaft 98 isa clutch plate 92 which cooperates with a back-up plate 94 mounted inabutment with a protruding shoulder 96. The clutch plates 92 and 94 arespaced apart and provided with friction driving faces 98 engageable withopposed faces of a sprocket or transfer wheel 100. The sprocket wheel100 is journalled on a sleeve bearing 102 and provided with outerprojecting teeth 104 so spaced that the receses therebetween engagelinks of a feed chain 106. The feed chain 106 includes a plurality ofprojecting fingers 108 which continue the advance of the individualclamp assemblies 38 after they leave the spiral grooves 84.

In operation of the bi-axial orientation machine of the invention, theweb 16 usually of a suitable stretchable plastic material is fed throughthe feed rollers 12 into the parallel entrance portion 32 of themachine. At this stage, the clamp assemblies are carnmed to the openposition by plate 77 and shortly thereafter as they advance are releasedso that serrations 80 tightly grip the edges of the web in arelationship initially perpendicular to the machine center line. As theclamp assemblies continue their travel through the entrance portion 32in a parallel path, they operate to pull the web through the machine andat the same time are free to pivot rearwardly to the axis of the webtravel in any angular amount up to 35 (the, amount of rearward freedombetween the stop lug 68 and the recess 70).

As the clamp assemblies 38 enter the stretching or diverging zone 34,they start their travel in an approximate angle of 20 relative to thelengthwise axis of the web. This 20 change in direction of each clampassembly as it enters the stretching zone is readily compensated for bythe ability of the clamp to pivot relative to its body portion 40.Therefore, as the clamp enters the divergent zone, no twisting of theedge of the web under the serration of the jaw is introduced.Furthermore, the pivoted relationship of the clamp swivel 50 relative tothe body portion 40 permits the clamp to lag or rotate as required afurther 15 to optimize and reduce stress concentrations along the edgeof the film web. Referring to FIGURE 6 wherein a small section of theweb edge is shown, it may readily be seen how the clamp swivels 50 haveassumed a lagging angle relative to their direction of travel along thedivergent guideways 18 and 20. Furthermore, in FIGURE 6 the optimizedstress reduction accomplished by the curved serrations 80 on the jaws ofthe clamps may readily be appreciated. In this view, the scalloped edgeof the web will be seen to approach the serrations in a generallytangentially direction at the edges of the jaw face. In prior artclamps, such as employed in the aforementioned patent, the straightdirection of the serrations along with the inability of the clamp topivot relative to its body portion created unduly large stressconcentrations in the areas adjacent the clamps which usually createdripping of the web unless highly optimized and controlled conditionswere maintained. Applicants invention has substantially reduced thecriticality of these operating factors and has produced a machinewherein commercial operation becomes practical.

A further feature of the ability of each of the clamps to pivot relativeto its body portion is that as the clamps travel along a curved patheither in the stretching zone or outside thereof they tend to haveuneven speeds and angles of tension relative to the edge of the web andrelative to the speed at which the roller 82 is being advanced by thefeed screw 86. Since all forces about each clam-p jaw are in balance andits pivotal freedom allows it to temporarily assume a speed difierentfrom the forward speed of its associated drive roller 82, there is lesschance of stress concentration and the possibility of the tearing of thefilm sheet is greatly reduced.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. In a bi-axial web stretching machine the combination comprising,means for feeding a web of material to and through a stretching zone,said stretching zone being defined by guide means arranged in adiverging relationship relative to the longitudinal axis and directionof travel of said web, and a plurality of clamping means movable alongsaid guide means for gripping the edge of said web and advancing saidweb through the stretching zone; each of said clamping means including abody portion having a lower projecting extension for engaging saidfeeding means for advancing said body portion along said guide means infixed relation thereto, elongated slipper bearing means'cooperative withsaid guide means for preventing rotation of said body portion relativeto said guide means, and clamping arm means pivotally mounted upon saidbody portion for engaging the edge of said Web, whereby said clampingarm means may rotate relative to said body portion while passing throughsaid stretching zone to thereby equalize any uneven speed of feed andangle of tension in said web and reduce stress concentrations in saidstretching zone.

2. The combination in accordance with claim 1 wherein said clamping armmeans includes a movable jaw portion, said jaw portion having aplurality of serrations in the plane of said web for engagementtherewith, said serrations being curved toward the central axis of saidweb and having end portions substantially tangent to the direction ofstress in the edge of said web adjacent said jaw portion whereby thelongitudinal stress in said web along the edge is substantiallyequalized between adjacent clamping means and continued under the faceof said jaw portion.

3. In a bi-axial web stretching machine the combination comprising,means for feeding an elongated web of material to and through astretching zone, said stretching zone being defined by guide meansarranged in a diverging relationship relative to the longitudinal axisand direction of travel of said web, and a plurality of clamping meansmovable along said guide means for gripping the edge of said web andadvancing said web through the stretching zone; each of-said clampingmeans including, clamping arm means having a movable jaw portion, saidjaw portion having a plurality of serrations in the plane of said webfor engagement therewith, said serrations being curved toward thelengthwise axis of said web and having end portions substantiallytangent to the direction of stress in the edge of said web adjacent saidjaw portion whereby the longitudinal stress in said web along the edgeis substantially equalized between adjacent clamping means and continuedunder the face of said jaw portion.

4. The combination in accordance with claim 1 wherein each said slipperbearing means includes a pair of interlocking U-shaped elementssurrounding a portion of said clamping means body portion.

5. The combination of claim 4 further including first and second legmeans extending outwardly from the body portion of each clamping means,said first leg means including a roller at each end in contact with anupper surface of said guide means, said second leg means including aroller at each end in contact with a lower surface of said guide meanswhereby rotation of said clamping means relative to said guide means inan axis perpendicular to the pivot axis of said clamping arm means isprevented.

6. Web securing means for use in a bi-axial stretching machine having astretching zone comprising, clamping arm means having a movable jawportion, said jaw portion including a plurality of serrations in theplane of said web for engagement therewith, said serrations being curvedtoward the central axis of said web and having end portionssubstantially tangent to the direction of stress in the edge of said webadjacent said jaw portion whereby the longitudinal stress in said webalong the edge may be equalized between adjacent clamping means andcontinued under the face of said jaw portion.

7. Web securing means for use in a bi-axial stretching machine having astretching zone comprising, securing means including clamping meansmovable along a guide means for gripping the edge of said Web andadvancing said web through the stretching zone; each of said clampingmeans including, clamping arm means having a movable jaw portion, saidjaw portion having a plurality of serrations in the plane of said webfor engagement therewith, said serrations being curved toward thelongitudinal axis of the web and having end portions substantiallytangent to the direction of stress in the edge of the web adjacent saidjaw portion whereby the longitudinal stress in said web along the edgeis substantially equalized between adjacent clamping means and continuedunder the face of said jaw portion.

8. Web securing means for use in a bi-axial stretching machine having adivergent stretching zone defined by spaced parallel guide means andfeeding means therebelow comprising, each of said securing meansincluding depending clamping means having a body portion including meansengaging said feeding means for advancing said body portion along saidguide means in fixed relation thereto, each of said clamping meansincluding elongated slipper bearing means cooperative with said guidemeans for preventing rotation of said body portion relative to saidguide means, and clamping arm means pivotally mounted upon said bodyportion for engaging the edge of the web, whereby said clamping armmeans may rotate relative to said body portion while passing through thestretching zone to thereby equalize any uneven speed of feed and angleof tension in said web and reduced stress concentrations in saidstretching zone.

9. The combination in accordance with claim 8 wherein each said slipperbearing means includes a pair of interlocking U-shaped elementssurrounding a portion of said clamping means body portion.

10. Web securing means for use in a bi-axial stretching machine having adivergent stretching zone defined by spaced parallel guide meanscomprising, clamping means for gripping the edge of said web andadvancing said web through the stretching zone of said machine, saidclamping means including a body portion enclosed by elongated slipperbearing means slidably movable between said spaced parallel guide meansfor preventing rotation of said body portion relative to said guidemeans, and clamp ing arm means carried by said body portion for engagingthe edge of said web, and means for mounting said clamping arm meansupon said body portion to prevent transmission of twisting movement ofsaid clamping arm means to said body portion whereby friction of saidbody portion along said guide means is reduced.

(References on following page) References Cited by the Examiner UNITEDSTATES PATENTS Jones.

Tooke et a1. 181 Koppehele 181 X Koppehele et a1. 181 Bruckner 181 83,150,433 9/1964 Kamp 2657 3,153,812 10/1964 Salsakbabara et a1 1813,195,177 7/1965 Kawamural et a1. 181

FOREIGN PATENTS 1,111,812 7/1961 Germany.

WILLIAM J. STEPHENSON, Primary Examiner.

1. IN A BI-AXIAL WEB STRETCHING MACHINE THE COMBINATION COMPRISING,MEANS FOR FEEDING A WEB OF MATERIAL TO AND THROUGH A STRETCHING ZONE,SAID STRETCHING ZONE BEING DEFINED BY GUIDE MEANS ARRANGED IN ADIVERGING RELATIONSHIP RELATIVE TO THE LONGITUDINAL AXIS AND DIRECTIONOF TRAVEL OF SAID WEB, AND A PLURALITY OF CLAMPING MEANS MOVABLE ALONGSAID GUIDE MEANS FOR GRIPPING THE EDGE OF SAID WEB AND ADVANCING SAIDWEB THROUGH THE STRETCHING ZONE; EACH OF SAID CLAMPING MEANS INCLUDING ABODY PORTION HAVING A LOWER PROJECTING EXTENSION FOR ENGAGING SAIDFEEDING MEANS FOR ADVANCING SAID BODY PORTION ALONG SAID GUIDE MEANS INFIXED RELATION THERETO, ELONGATED SLIPPER BEARING MEANS COOPERATIVE WITHSAID GUIDE MEANS FOR PREVENTING ROTATION OF SAID BODY PORTION RELATIVETO SAID GUIDE MEANS, AND CLAMPING ARM MEANS PIVOTALLY MOUNTED UPON SAIDBODY PORTION FOR ENGAGING THE EDGE OF SAID WEB, WHEREBY SAID CLAMPINGARM MEANS MAY ROTATE RELATIVE TO SAID BODY PORTION WHILE PASSING THROUGHSAID STRETCHING ZONE TO THEREBY EQUALIZE ANY UNEVEN SPEED OF FEED ANDANGLE OF TENSION IN SAID WEB AND REDUCE STRESS CONCENTRATIONS IN SAIDSTRETCHING ZONE.